The study is designed to evaluate transmural myocardial perfusion at rest and during exercise in intact awake dogs with chronic stable left ventricular hypertrophy. Since coronary perfusion occurs predominantly in diastole, studies will be performed in dogs in which left ventricular hypertrophy has been produced by constriction of the ascending aorta (in which diastolic aorta pressure remains at normal or near normal levels), as well as by production of renal hypertension (in which diastolic aortic pressure is elevated). Myocardial perfusion dynamics will be studied when the hypertrophy-inducing stress is imposed in puppies (so that myocardial hypertrophy evolves during the period of growth), as compared with adult dogs, to evaluate the functional significance of previously reported morphologic evidence indicating that when cardiac hypertrophy occurs in adult animals growth of the coronary vasculature may not keep pace with the increase in muscle mass. The long-term goal of this research is to delineate factors which may be responsible for the clinical and pathologic evidence of subendocardial ischemia which is commonly found in patients with chronic left ventricular hypertrophy.